The disclosure of Japanese Patent Application No. 2000-244490 filed on Aug. 11, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a capacitance-type human body detector for use outdoors for detecting a human body and, more particularly, to a human body detector capable of distinguishing a human body from raindrops.
2. Description of the Related Art
A technology capable of detecting approach of a human body is disclosed in Japanese Patent Application Laid-Open No. 10-308149, wherein a human body detecting sensor is disposed in a hollow door handle of a vehicle so as to detect a user approaching the vehicle. Furthermore, a generally-termed smart entry system for locking and unlocking a door of a vehicle when a user carrying a wireless transmitter approaches or moves away from the vehicle is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 7-189538 and 10-306639.
However, in systems as mentioned above, it is necessary to prevent a door from being unlocked when a user merely passes by the vehicle without an intention of opening the door.
Therefore, consideration has been given to a technology in which a capacitance-type sensor for detecting a human body is provided in a door handle, and the door unlocking is performed based on the AND of an output of the human body-detecting capacitance-type sensor and a signal from a wireless transmitter.
However, if a human body-detecting capacitance-type sensor is provided in a door handle, there is a problem of false detection of a human body caused by raindrops striking the door handle. More specifically, in a capacitance-type sensor, a capacitance detecting portion is provided in, for example, a door handle grip, and a change in the detected capacitance is recognized. That is, when a human hand contacts the handle grip, the stray capacitance of the human hand changes the capacitance. Therefore, upon such a capacitance change, the sensor detects contact of a human hand with the handle grip. However, the stray capacitance of a raindrop also changes the capacitance of the sensor. Therefore, in some cases, a raindrop causes detection means of the sensor to make a false detection, thus leading to useless generation of a human body detection signal or a request signal to a wireless transmitter carried by a user.
It is an object of the invention to provide a human body detector capable of distinguishing between a raindrop and a human body.
A first aspect of the invention is a human body detector including a capacitance-type sensor that a human body contacts, and detection means for receiving an output of the capacitance-type sensor, and distinguishing the human body from a raindrop and detecting only the human body based on an output frequency of the output.
A second aspect of the invention is a human body detector including a capacitance-type sensor that a human body contacts, and detection means for receiving an output of the capacitance-type sensor, and distinguishing between the human body from a raindrop and detecting only the human body based on a change in the output within a predetermined time.
According to the first and second aspects of the invention, when a dielectric object, such as a human body or the like, contacts the capacitance-type sensor, the capacitance of the capacitance-type sensor changes, so that the output of the sensor changes. The output frequency and the changing rate of the capacitance vary depending on objects. Therefore, the output change of the capacitance-type sensor varies depending on objects detected. More specifically, for example, when the capacitance-type sensor detects a raindrop, the output of the sensor reduces by a predetermined amount in at most 5 msec (in frequency, at least 200 Hz). In contrast, when the capacitance-type sensor detects a human hand that is not wet, the output of the sensor reduces by the predetermined amount in about 10 to 50 msec (in frequency, about 100 to 20 Hz). Thus, the changing rate (frequency) of the output differs between a raindrop and a human body. The detection means distinguishes objects based on the aforementioned characteristic. That is, the detection means calculates the changing rate or frequency of the output, and determines whether the changing rate (frequency) is the changing rate (frequency) that occurs when a human body is detected. If it is determined that the calculated changing rate is the changing rate (frequency) caused by a human body, the human body detector outputs a human body detection signal.
Therefore, according to the first and second aspects, the human body detector is able to distinguish between a raindrop and a human body, and therefore does not make a false detection based on a raindrop, therefore does not commit an error of unlocking to the door.
In the second aspect, the detection means may allows a voltage to pass if a changing rate of the voltage is in a predetermined band.
Therefore, the detection means stores the changing rate of voltage that occurs when a human body contacts the capacitance-type sensor. The changing rate of voltage may be determined by using a time needed for a predetermined amount of voltage reduction, or may also be determined by using an amount of voltage reduction in a predetermined time. In an example herein, the former method is adopted. For example, the changing rate that occurs when 40 msec is needed for a predetermined amount of reduction of voltage is stored in the detection means. When a human body contacts the capacitance-type sensor, the detection means calculates a changing rate of voltage, and detects that the calculated changing rate is within the stored band of changing rate, and then outputs a human body detection signal. If the capacitance of the capacitance-type sensor is changed by a raindrop, the detection means acquires the changing rate of voltage, and determines whether the acquired changing rate is a changing rate stored. In the case of a raindrop, because the voltage of the sensor reduces by a predetermined amount in at most 5 msec, the detection means detects that the acquired changing rate of voltage is not within the band of changing rate, so that the human body detection signal is not outputted. If the capacitance of the capacitance-type sensor is changed by an outside air temperature change, the detection means acquires a changing rate of voltage, and determines whether the acquired changing rate of voltage is a stored changing rate of voltage. As for the outside air temperature change, the predetermined amount of reduction of the voltage requires a time that is far longer than, for example, 500 msec. Therefore, the detection means detects that the acquired changing rate of voltage is not within the stored band of changing rate of voltage, so that the human body detection signal is not outputted.
Therefore, according to this aspect of the invention, even if the capacitance of the capacitance-type sensor changes due to a raindrop, an outside air temperature change or the like, the human body detector does not output the human body detection signal. The human body detector detects only a human body, and detects the human body detection signal.
The human body detection signal avoids an event that a raindrop or the like is falsely detected and the door is unlocked.
Therefore, the human body detector can be effectively used outdoors.
In the foregoing aspects of the invention, the detection means may include a band-pass filter.
Therefore, a condition for allowing voltage to pass through the band-pass filter provided in the detection means is that the changing rate of the voltage be within a band of changing rate of voltage needed for detection of a human body (a band of changing rate that occurs when the predetermined amount of reduction of voltage requires 10 to 50 msec). If frequency is used instead, a similar effect can be achieved by employing a band-pass filter that allows passage of frequency of 100 to 20 Hz corresponding to time of 10 to 50 msec.
Therefore, according to this aspect, even if the human body stray capacitance varies depending on persons, a human body can be reliably detected, and the detection accuracy can be improved.
In the foregoing aspects, the human body detector may be disposed in a door handle of a motor vehicle, and may detect a contact between the door handle and the human body.
If the human body detector is disposed within a door handle disposed on an outer side of a door, a human body does not directly contact the human body detector, so that the human body detector is made less liable to failure.